I'm doing my project on energy based auditing, it's an industrial project... I need to measure the high voltage of around 240v, can I step down to 5v using voltage divider?
You can't accurately measure energy flow without measuring the instantaneous voltage and instantaneous current with many samples per cycle.
I suggest you take a look at reference designs for energy meters. If it's an industrial situation you may have to do it for 3-phase power. The safest and most expensive method is via a potential transformer.
Yes you can. But things become complicated quickly since there are a few other things to consider.
When you design such circuit you'd want to have as much resistance as possible to limit wasted power in the divider. You'd also want your divider to survive electrical fast transients (EFT) and other surges, thus your divider should be able to withstand those voltages.
But high total resistance makes common mode and noise pickup a problem. Yet low total resistance make dissipated heat a problem.
You could take 20 resistors to combat this, but then you'd also have the side effects of 20 resistors. (eg: space, inaccuracy and drift)
Then you also have the problem of data acquisition, since you'd need to be doing RMS with enough bit depth and sample-rate. Which is quite cpu intensive.
And then the harmonics show up and your measurement is incorrect...
Notice that whenever you attach anything to live or neutral without high resistance or isolation you can't directly attach anything else anymore. No programmer without isolation, no USB, no oscilloscope.
Magic smoke will be released if you do.
Your cheapest solution would be a two stage step down transformer with a buffer in between; most commercial transformers are highly efficient and would save you the further trouble of worrying about noise.
Just a thought but since your goal seems to be measuring energy rather than voltage, why don't you concentrate on measuring current and just assume the voltage is its nominal value. You didn't specify accuracy but mains voltage rather varies more than about 5% either above or below nominal. This would eliminate a difficult, and potentially dangerous, measurement process. Measuring current is not necessarily easy but it seems you must do it since energy is much more dependent on current rather than voltage.